Earth's global 'climate sensitivity,' is a fundamental quantitative measure of the susceptibility of Earth's climate to human influence. A landmark report in 1979 concluded that it probably lies between 1.5‐4.5°C per doubling of atmospheric carbon dioxide, assuming that other influences on climate remain unchanged. In the 40 years since, it has appeared difficult to reduce this uncertainty range.

In this paper, S. Sherwood and colleagues thoroughly assess all lines of evidence including some new developments. They found that a large volume of consistent evidence now points to a more confident view of a climate sensitivity near the middle or upper part of this range. In particular, it now appears extremely unlikely that the climate sensitivity could be low enough to avoid substantial climate change (well in excess of 2°C warming) under a high‐emissions future scenario. The researchers remain unable to rule out that the sensitivity could be above 4.5°C per doubling of carbon dioxide levels, although this is not likely. Continued research is needed to further reduce the uncertainty and they identified some of the more promising possibilities in this regard.

An assessment of Earth's climate sensitivity using multiple lines of evidence